The Hajj is a sequence, and the sequence is the obligation. It cannot be performed early, late or in a different order.
The pilgrim enters ihram at or before a miqat, one of the fixed boundary points around Mecca, putting on the two unsewn white cloths in the case of men and ordinary modest dress in the case of women, and taking on the associated restrictions: no cutting of hair or nails, no perfume, no hunting, no sexual relations, no quarrelling.
Tawaf is seven circuits of the Kaaba, anticlockwise, beginning at the Black Stone. Sai is seven passages between the hills of Safa and Marwa, now enclosed within the mosque, recalling Hagar's search for water for Ishmael and ending at the well of Zamzam.
On the eighth of Dhu al Hijjah the pilgrims move out to Mina. On the ninth comes the wuquf, the standing at Arafat from midday until sunset, and this is the Hajj: a hadith states that the Hajj is Arafat, and a pilgrim who misses it has not performed it, whatever else they have done. That night is spent at Muzdalifah in the open, gathering pebbles.
On the tenth the pilgrim stones the largest of the three jamarat pillars at Mina, offers or arranges an animal sacrifice, and shaves or shortens the hair, at which point most ihram restrictions lift. Then the tawaf al ifada at the Kaaba. Two or three further days at Mina involve stoning all three pillars, and the pilgrimage ends with the tawaf al wada, the farewell circuit.
Three of these stations, Arafat, Muzdalifah and Mina, are open ground rather than buildings, which is why the Hajj is an encampment as much as a visit.